Moderate stream rises along the Onkaparinga River after 25-35 mm fell in the 24 hours to 9 am this morning (Bureau).

In Addition:

Hypothesis  Higher Probability of a Colder Winter Outbreak for Southeast Australia by the End of June 2014, into Early July, Observation Based

[Edited for clarity]

Written Monday, 16th of June 2014, updates where indicated:

As I understand, recent observable shifts in sub-polar rossby-wave [low] activity suggest the ridging (which is currently disrupted in the Southeast) is leading to an increase in the passage of troughs and sharper pressure gradients [across the Bight]. The lower atmospheric volume (due to a reduction in day-time maxima, and increase in dew points) also appears to be affecting these pressure gradients, and encouraging moist off-shore Southern Ocean wind currents from the Southwest. This further seems to be inducing orographic lifting and cloud-cover further inland. Calmer more stable conditions over the Southwest (near Perth) may follow suit as the recent zonal sub-tropical and sub-polar 200 hPa wind currents become more meridional (Bureau, update 17th  front crossing the SW WA coast). The fact that, for the past week or so, near-zero, zero, or sub-zero minima have (for the most part) declined in frequency also seems to support a case [for] higher dew points and more cloud-cover.

Changes near Perth may affect rossby-wave activity in the east through the current zonal [West-East] continental high-pressure system shifting to meridional [North-South], allowing sharper pressure gradients (associated with strong fronts or cut-off lows) to move further east.

Rainfall for the this time of year (June) is well below average, with less than 30 mm recorded to date (17th), in a month that can average between 90 and 120 mm.

Update 19th (Thursday)  model outputs GFS/ACCESS-G +96 HRS MSLP, THK, PRECIP 1000 EST Monday 23rd of June 2014 appear to suggest that as slow cut-off lows become less prevalent and a meridional pattern [of lows] starts to develop more robustly in the Southern-Ocean sub-polar region, there is an increasing likelihood of a strong cold front (or two) reaching the Southeast Quadrant [of Australia]. This could mean possible falls of 20-40 mm over a 2-3 day period (in some places more), with a further increase in totals over a period of up to a week. Sometime around the 23rd of June, GFS (19th) is implying the 1000-500 mb thickness will fall sharply during the day, possibly generating temperatures well below 10 degrees C (at this early stage, a solid 3 days out). This implies freezing rain or even sleet. My impression is the meridional sub-polar pattern [jet] needs to become firmly established for this to be possible at low altitude (0-400 m).

Update 20th (Friday)  [there is a] slight change in the ACCESS/GFS outputs, scenarios mostly maintained per previous description; 1000-500 mb thickness still possible sharp decline. At this stage Id be expecting moderate rain with some heavier bursts and embedded instability [CAPE in latest GFS runs does not seem significant, however this does not rule out embedded thunderstorms along a pre-frontal trough]. Wind speed will undoubtedly be a factor with the system likely to traverse the Southeast Australia rather quickly (both models). As the thickness reduces more, moisture can be moved into a region to facilitate lower pressure, although strong NW winds ahead of a trough could generate fickle conditions until a pressure gradient becomes more prevalent.

The key to this system [starting the 23rd] being robust, in my view, and actually generating 20-40 mm or more in the respective regions (south of 30 degrees latitude) is a synchronicity between the westerly belt [a short-wave upper-level low] and the sub-tropical 200 hPa winds. The GFS +72 HRS sfc PWAT, VVEL 700 hPa implies this is likely, the VVEL turning strongly negative, favouring pre-frontal thunderstorm activity (20th and 21st, GFS). According to GFSs 06z run, 21st of June, the thickness is likely to plummet to somewhere between 5370 to 5340 metres [NOAA], which probably seems enough for hail at elevation (0-1000 m). CAPE has remained similar.

I would think there could be a significant change in soil moisture with slight-to-moderate change in surface runoff if the forecast dynamics hold [assuming the rain rate does not outpace infiltration], with the [second] front currently crossing SW WA (21st). With the amount of cloud-cover around as this change approaches, I do not think it would be unexpected if the evaporation rate fell markedly during the 23rd.

GFS (22nd of June) indicates the approaching system here is not supported by either higher specific humidity or precipitable water, however the vertical component of the 200 hPa winds is getting quite strong with increased CAPE and instability ahead of strong surface winds [likely to occur around Central SA area ~23rd]. My further impression is this is a thunderstorm-type system.

Update 22nd (Sunday)  Changes in stream flow have been mostly borderline or slight since autumn; would be expecting 15-20 mm overnight from the approaching system, 5-10 mm over the following 2-3 days, tapering off to 1-5 by Thursday, system total 25-50 mm by Thursday; more widespread south of 30 degrees latitude. I would think there could be a moderate-to-significant change in soil moisture, and slight-to-moderate change in run-off.

Update 25th (Wednesday)  It seems apparent [at this stage] there is a chance of a colder more robust event circa the 27th of June, with the long-wave surface rossby-wave pattern rotating to anchor the westerly belt [over the coming 7 days] into synchronicity with tandem upper-level lows [situated North-South, south of the Bight, ACCESS-G]. This meaning the 3 main upper-level lows over Antarctica on the Bureaus 200 hPa wind and direction forecasts have drifted east and west from the Indian and Pacific Oceans Respectively. If this system (the lower-latitude upper-level low with a front) reaches the Southeast, it is possible additional falls of 20-40 mm could be recorded in Central SA on Friday afternoon [ACST]. The change in thickness during the morning (GFS shows something like 150-200 metres, NOAA) may signal a dramatic fall in the day-time temperature from perhaps 12-13 degrees C to 3-4 degrees C (based on recent observations). The impact on stream flow could start to become more noticeable after 10-15 mm with moderate stream rises in addition to the moderate rises already observed on Tuesday (24th).

Update 28th  Another 31.1 mm to 9 am with moderate stream rises overnight, no flooding; moisture is still soaking in, implying the rain rate was in excess of the infiltration rate. A GFS forecast run circa the 22nd of June suggested this could happen. The temperature yesterday averaged around 7 degrees C and didnt really go much lower (~6-8 degrees C).

Update 29th  A further 1.5 mm to 9 am brings the system total (27th to 29th) to 32.6 mm, and the monthly total to 139.8 (above average). Our annual total is now 438.5 (update 1st July), which is more than half the annual average (approx. 840-860 mm).

Update 3rd July (Thursday)  In the last few days (30th June  2nd July) the day-time minima have again fallen to near zero degrees. With this in mind as the maxima remain mostly steady (the barometric pressure rising), it appears (after consecutive systems between the 20th and 30th with significant pressure gradients) there is a much stronger case for a change (increase) in evaporation rates circa the 8th to 9th of July (GFS/ACCESS-G +144 HRS). This may be similar to what occurred 27th-28th of June. Less cloud-cover (particularly low- and middle-level) seems more likely on the 7th or 8th (or both), the thickness falling to well below the 5400 metres required for hail at sea-level (GFS). [My view is] hail is probably highly-likely with a greater chance of frosts in the initial days before rain falls (as the relative humidity plummets).

The system circa 8th-9th of July seems unlikely to have elevated CAPE. The sub-polar jet could become a more noticeable factor [Bureau Interactive 200 hPa winds] as cold, moist maritime air is drawn up from the south. In my view (3rd of July), rainfall may be anywhere from 50 to 70 mm at the lower end of the range, up to 120 mm by the following Friday [11th of July, widespread through the Adelaide Hills and higher ground along coastal areas]; impacts on flow [runoff] in the moderate-to-significant range. The diurnal temperature range is likely to narrow by the 9th [GFS, 3rd].

Update 4th July (Friday)  Little apparent change in the GFS [NOAA/WZ]. This system (8th-9th of July) does not seem supported by higher precipitable water or pressure vertical velocity (and associated CAPE). It appears thoroughly in the westerly belt with a contribution [on the Bureaus interactive maps] from both the sub-tropical and (to a lesser extent) sub-polar 200 hPa winds.

Update 6th July (Sunday)  3 mm recorded 12 am to 5.50 pm ACST (4th July), with another 3 to 9 pm, and 7.1 to 10 am on the 6th  monthly total stands at 13.1. There may be significant rainfall within the next 1-2 weeks.

Update 7th July (Monday)  Little change, perhaps a greater chance of getting very cold maxima over the next week compared to the last 2-3 [GFS, NOAA]. Flood Watch issued by the Bureau noted 5:13 pm ACST. Conditions may be very cold with higher dew points in general across elevated ground near the coast in the Southeast on or around the 11th.

River is starting to rise, again, somewhat similar to last night. Another 10.8 mm, 9 am to 11 pm CST. Sporadic heavy showers with some hail on-off. River water level might approach previous peak quicker at this rate . Ground underfoot is saturated with large puddles.

River is starting to rise, again, somewhat similar to last night. Another 10.8 mm, 9 am to 11 pm CST. Sporadic heavy showers with some hail on-off. River water level might approach previous peak quicker at this rate . Ground underfoot is saturated with large puddles.

54 mm to 9 am this morning. Another moderate rise in the river level to just below the peak of the previous peak (8th-9th) .

In my view [15th of July], there is the potential for a significant change in run-off circa Thursday morning (17th of July), in excess of 50 mm. Temperatures following this rain [period] may drop well below average [GFS].

In my view [15th of July], there is the potential for a significant change in run-off circa Thursday morning (17th of July), in excess of 50 mm. Temperatures following this rain [period] may drop well below average [GFS].

Cracked 100 mm for the month last night at 8.30 pm CST (100.8 mm after 14 mm in 3.5 hours). Another mm to 9 am followed by 12 to 5 pm, giving 113.8 mm to 5 pm, ground is saturated with deep puddles in some areas.

In my view [15th of July], there is the potential for a significant change in run-off circa Thursday morning (17th of July), in excess of 50 mm. Temperatures following this rain [period] may drop well below average [GFS].

Cracked 100 mm for the month last night at 8.30 pm CST (100.8 mm after 14 mm in 3.5 hours). Another mm to 9 am followed by 12 to 5 pm, giving 113.8 mm to 5 pm, ground is saturated with deep puddles in some areas.

2 moderate increases in [local Onkaparinga] streamflow between Wednesday the 16th and Friday the 18th of July 2014.

Another potentially-significant change in flow seems possible overnight into Thursday morning with a sharp increase in the relative humidity likely within 24 hours, accompanied by a moderate fall in the barometric pressure (GFS).

An area somewhere between Benalla and Seymour in Victoria based on recent GFS runs (00z and 06z respectively, 24th of September) may see as much as 50-60 mm over the next 24-48 hours, with possibly significant changes in soil moisture and direct run-off. The 06z run indicates up to 0.9 to 1.1 kg/m2 direct surface run-off. 1 kg/m2 is around 1 mm of water covering a square metre.

The local dew point in this region may incline overnight if it is not already doing so.

An area somewhere between Benalla and Seymour in Victoria based on recent GFS runs (00z and 06z respectively, 24th of September) may see as much as 50-60 mm over the next 24-48 hours, with possibly significant changes in soil moisture and direct run-off. The 06z run indicates up to 0.9 to 1.1 kg/m2 direct surface run-off. 1 kg/m2 is around 1 mm of water covering a square metre.

The local dew point in this region may incline overnight if it is not already doing so.

Highest falls recorded in the region were to the west of Seymour and east of Benalla (e.g. 81 mm in the 24 hours to 9 am at Rochester [BoM site 80049], 53 mm in the same period at Barnawartha [BoM site 82000]).

61 mm recorded in the same timeframe at Strathfieldsaye [BoM site 581018] east of Bendigo. There was a small change in stream flow [a peak] at Tallangatta Creek at McCallums.

The following is opinion based on model outputs;There appears to be an increasing likelihood (GFS) of greater than 40 mm in the Wagga Wagga area over the next 24-48 hours facilitated by the passage of a frontal system across the Bight towards Tasmania. Trough-like conditions are likely form (or have already done so) across south-west NSW and north-east VIC. This is may lead to a significant increase in dew points indicating higher relative humidity and precipitable water. The associated pressure gradients will probably sharpen in the next 24 hours across the affected region with the possibility of flash flooding by Tuesday morning.

The following is opinion based on model outputs;There appears to be an increasing likelihood (GFS) of greater than 40 mm in the Wagga Wagga area over the next 24-48 hours facilitated by the passage of a frontal system across the Bight towards Tasmania. Trough-like conditions are likely form (or have already done so) across south-west NSW and north-east VIC. This is may lead to a significant increase in dew points indicating higher relative humidity and precipitable water. The associated pressure gradients will probably sharpen in the next 24 hours across the affected region with the possibility of flash flooding by Tuesday morning.

Falls of greater than 50 mm recorded further east in the Cann and Genoa Region -- slight change in flow apparent [Bureau].

Written 16th of October 2014 [modifications]:In summary, observationally, there may be a chance the MJO [Madden-Julian Oscillation] over the tropics to the north is contributing to the development and redevelopment of a thickness and/or [500 hPa] higher-pressure anomaly in that region [near Broome, through the formation and reformation of multiple higher-pressure cells along the Equator], affecting the transition of 200 hPa sub-tropical winds [by leading them to become shallower], which in turn is affecting the generation of north-west cloud-bands. The next couple of weeks are, in my view at this stage [16th], likely to be fine with fickle, intermittent periods of instability conducive to thunderstorm activity, that is 16th to 30th of October 2014, which may be extended to the 3rd or 4th of November. Rains possible during the period after the 3rd or 4th may see a rise in the dewpoint and fall or moderation in both the day-time maximum and night-time minimum temperature  whether rainfall reaches the 20-40 mm range remains to be seen.

13th of November  Next time the thickness / 500 hPa feature seems likely to be displaced enough for the south-westerly rossby-wave.

Longer-term change in displacement of 500 hPa feature near Kimberly / Broome is taking a while. Maybe upper low at 500 hPa nearing Perth around that time could become more dominant as forecast [ACCESS-G +144 HRS]? Who knows?

One thing that seems not good for Central QLD dry conditions / Northwest NSW - the near-surface winds seem to reverse from south-easterly to north-westerly by the 14th, then some impact / relief from the south-westerly change by 15th.

=> The observation that on both the ACCESS-G and GFS model runs during the latter period of October, a higher-pressure / thickness feature was situated with a peak upper-high over the Broome / Kimberly in Northern WA.

=> North-westerly winds off the western flank of the TH / UR5 all the way to the Tasmanian west coast. The TH / UR5 seemed to have a range (peak) between about Broome and Central-western NSW. In combination with this feature a T / UL5 appeared to form off the coast of Perth, contributing to maximum wind speed near Geraldton.

=> The uniform absence of the both these [500 hPa] features suggested dominant rossby-wave activity from the Southern Ocean and greater likelihood of significant rain (depending on the shape of the TH / UR5 and T / UL5 on the ACCESS-G and GFS charts). Their prevalence suggests dominant [near-surface] NW / SE winds across the continental interior and troughing along the west coast.

=> During 2-3 days of escalating strength and then dissipation of the TH / UR5 feature there can be a near-surface high-pressure area over the Southeast, directing south easterlies inland, generating lower-humidity and higher-temperature conditions across Central QLD and parts of inland NT / SA, which are evident on the ACCESS-G and GFS Screen Temperature, Dewpoint and Wind Prognoses.